Aromatic amines such as aniline are useful in a variety of applications, such as in the preparation of dyes, herbicides and as antiknock agents for spark-ignited gasoline powered internal combustion engines. In the past, they have been prepared by reducing nitro aromatics, such as nitrobenzene. This is a very useful method of preparation, but depends upon the ready availability of the proper nitro aromatic which, in some cases, is not available. Another method is described by Van Verth et al, U.S. Pat. No. 3,219,702, wherein a cyclohexanone is reacted with an ammonia compound in the presence of a hydrogen acceptor (e.g., a nitrobenzene) and a dehydrogenation catalyst. Since the main reactant in this process is a cyclohexanone, its utility depends upon the availability of the appropriate cyclohexanone.
In Wilder et al, U.S. Pat. No. 3,219,704, a similar process is described which differs in the omission of the hydrogen acceptor and the requirement of an amount of the cyclohexanone at least equivalent to the amount of ammonia compound present.
Another process is described in Barker, U.S. Pat. No. 3,272,865, which involves the reaction of a hydroxybenzene with ammonia or amine in contact with a silica-alumina, titania-alumina, zirconia-alumina, phosphoric acid or tungsten oxide catalyst. This process is quite similar to that described by Neuroessen, in U.S. Pat. No. 1,935,209, and by Lowy et al, in U.S. Pat. No. 1,449,423.
In Barker, U.S. Pat. No. 3,442,950, another process is described involving the reaction of a cyclohexanol with an aminating agent in the presence of a catalyst. If cyclohexanone is present in the cyclohexanol, hydrogen must be added in an amount at least sufficient on a molar basis to convert the cyclohexanone to cyclohexanol.
Other processes for making aromatic amines are taught by Ballard, U.S. Pat. No. 2,413,598; Vogt, U.S. Pat. No. 2,013,873; Groggins, "Unit Processes in Organic Synthesis," 5th Edition; and Houben-Weyl, "Methoden der Organische Chemie," Vol. 11/1, pages 117-122.